I'm gonna glom on to this one since it's titled diffusion.
I've only just begun making CO2 for the tank, but have been brewing for years. Generating the CO2 is not an issue.
Diffusing it, however...
What I've done today is drill a hole it the bottom of the HOB intake pipe and inserted the discharge end of the CO2 hose into it. As the HOB draws up water, it carries the CO2 with it. The impeller in the HOB chops up the CO2 bubbles, dumps them and the water into the filter box, the CO2 laden water passes through and over the filters, and spills over into the tank. Sounds good. What do y'all think?
I do imagine some of the CO2 escapes in the short waterfall.
Since the HOB is more of a water lifter, and not a centrifugal pump, I'm not worried about entrained gas causing cavitation and the problems that come with that, but I can hear when bubbles pass through the impeller chamber. They be gettin chopped, yo.
Has anyone done this and worn out the impeller or motor prematurely?